The invention relates to binders for cathodically depositable coating compositions for the electrocoating lacquering process using cationic synthetic resins.
The electrophoretic deposition of synthetic resins on electrically conductive substrates, which is called the electrocoating lacquering process, is known and is widely used. Here, in particular the cataphoretic process, in which cationic resins are deposited onto a substrate connected as the cathode, offers advantages which have been described in the literature and with which an expert is very familiar. The synthetic resins used as binders in the process can contain ammonium, sulfonium or phosphonium groups.
It is also known to use copolymers of monomers having basic groups and other monomers as binders for cationic electrocoating lacquers.
The synthetic resins mentioned have been described, for example in German Auslegeschrift No. 2,075,799, German Offenlegungsschrift No. 2,634,211, German Offenlegungsschrift No. 2,603,666 corresponding to U.S. Pat. No. 3,984,299, German Offenlegungsschrift No. 2,531,960, corresponding to U.S. Pat. Nos. 4,101,486 and 4,134,816, German Offenlegungsschrift No. 2,265,195 corresponding to U.S. Pat. Nos. 3,947,339; 4,017,438; 4,104,147; and 4,148,772, German Offenlegungsschrift No. 2,252,536, German Patent No. 1,546,840 corresponding to U.S. Pat. No. 3,455,806, German Patent No. 1,546,854 correspondng to U.S. Pat. No. 3,458,420, German Auslegeschrift No. 2,320,301, German Offenlegungsschrift No. 2,554,080, corresponding to U.S. Pat. No. 4,260,697, German Auslegeschrift No. 1,930,949 corresponding to U.S. Pat. No. 3,729,435, German Offenlegungsschrift No. 2,707,482, corresponding to U.S. Pat. No. 4,320,220 and German Offenlegungsschrift No. 2,732,902, corresponding to U.S. Pat. No. 4,176,099.
As a rule, acids are used to neutralize the cationic resins completely or partially, in order to make them water-soluble or dispersible in water. The dispersions, if appropriate after pigmentation and addition of fillers, flow auxiliaries, low proportions of organic solvents and other known auxiliaries, can then be deposited, on application of a voltage, onto the substrate connected as the cathode. After stoving of the deposited film, a coating is thus obtained which protects against corrosion.
Commercially available emulsion polymers, although readily preparable by emulsion polymerization, cannot, as a rule, be used as binders for electrocoating lacquers.